Igniter composition comprising pyrotechnic dispersion in solid propellant



United States Patent 3,234,059 IGNITER COMPOSITION COMPRISING PYRO-TECHNIC DISPERSION IN SOLID PROPELLANT Wayne A. Proell, Seymour, Ind.,assignor to Standard Oil Company, Chicago, 11]., a corporation ofIndiana No Drawing. Filed Nov. 18, 1963, Ser. No. 324,247 8 Claims. (Cl.149-19) This invention relates to an igniter composition for solidpropellants and more particularly to an igniter composition comprisingan admixture of a pyrotechnic and a solid propellant composition.

The development of a satisfactory igniter for propellant systems hasbeen very desirable. Igniters suitable for the ignition of rocketengines and associated devices, such as starter cartridges, have reliedin many instances upon complex granular or pelleted pyrotechnicmaterials. In general, the eificiency of these igniters has variedconsiderably, with even the best requiring a large amount of ignitercharge, showing low reproducibility, and generating dirt and smoke.Furthermore, these igniters require care in loading in order to obtainconsistent results, are moisture sensitive due to their granulartexture, show a poor temperature coefficient, and charge characteristicswith age.

It has been discovered that an igniter composition made up of acompacted, dense admixture of pyrotechnic, such as gunpowder; and asolid propellant, such as an ammonium nitrate propellant, compressedinto a coherent cake having the propellant as an essentially continuousphase, exhibits improved results upon ignition in respect to many of theabove problems. This is surprising, as .the solid propellant is not anigniter and might be predicted to reduce the burning to such a lowdegree that the combination would not be an igniter.

In addition, the inventive igniter composition exhibits a highlyreproducible performance of burning times in a range not generallypossible with mechanical mixtures of pyrotechnics. This permits easierformulation of the igniter composition and provides greater expectancyof a predetermined performance.

The inventive igniter composition is a compacted, dense admixturecomprising a dispersion of pyrotechnic in an essentially continuousphase of a solid propellant. This means that the dispersion of thepyrotechnic is essentially surrounded by the solid propellant. It isdesirable that the propellant of the admixture exhibit a low porosity,usually less than about 8% and preferably less than about 4%. Theadmixture includes a pyrotechnic such as gunpowder, aluminumpowder-alkali perchlorate, nitrocellulose grains, and boronpowder-potassium nitrate, preferably gunpowder and boronpowder-potassium nitrate and especially gunpowder. In many instances,the pyrotechnic is granular and porous. Its porosity may range up toabout 50% but preferably is lower.

The admixture also includes a solid propellant, present as essentially acontinuous phase. An especially suitable propellant is the ammoniumnitrate propellant which is primarily made up of ammonium nitrate, anoxidizable organic binder material, and a combustion catalyst.

The ammonium nitrate propellant has been previously described in US.2,999,462 and copending application S.N. 715,987 filed February 18,1958, now Patent No. 3,148,096, which are incorporated into and made apart of this specification. In general, the ammonium nitrate propellantcontains ammonium nitrate as the predominant component usually inamounts in excess of about 60 weight percent, an oxidizable organicbinder, usually between about 10 and about 40 weight percent; and acatalyst, usually between about 0.5 and about 10 weight percent.

The oxidizable organic binder is utilized to permit the shaping of theammonium nitrate composition into definite configurations and to consumethe excess oxidizing power of the ammonium nitrate. A binder may be asingle compound; such as rubber or asphalt, or a mixture of materials,commonly a polymeric base material (such as cellulose acetate) and aplasticizer for the base material. Both thermoplastic and thermosettingmaterials may be utilized as the binder. Many of the commonthermoplastic materials are identified in the above cited references.Polyurethane serves to illustrate a thermosetting material which issuitable as a binder material.

In addition to the catalyst covered in the above references, suitablecatalysts include alkali metal salts of nitriloacetic acid, anthranilicacid, and nitrosalicylic acid; and amine salts of nitrosalicylic acid.Commonly, the alkali metal salt is the sodium salt, and the amine saltis prepared from piperazine or guanidine.

In addition to the basic components, i.e., ammonium nitrate, binder andcatalyst, the ammonium nitrate propellant may contain other commonlyutilized materials such as asphalt and carbon to improve coldtemperature ignition, and amines to chemically stabilize the propellantagainst decomposition in hot storage. These additional components aredescribed in the above cited copending application S.N. 715,897.

It is desirable that the admixture contain about 20 to 60 weight percentof the pyrotechnic and about 40 to weight percent of the solidpropellant. Especially suitable admixtures have about 30 to 50 weightpercentof the pyrotechnic and about 50 to 70 weight percent of thepropellant, especially when the pyrotechnic is gunpowder and thepropellant is ammonium nitrate propellant. Particularly suitablecombinations of gunpowder and ammonium nitrate propellant are 45%gunpowder and 55% propellant, and 40% gunpowder and 60% propellant.

The pyrotechnic and propellant are mixed together and pressed orotherwise treated until the propellant of the admixture is a compact,dense mass having a low porosity normally below about 8%. Compressionmolding is usually 'very suitable in most instances, although when thepropellant utilizes a thermosetting such as polyure: thane, theadmixture is usually cast. Usually, the pyrotechnic is in grain-form, towhich the propellant is added. It is preferred that the water absorbedor adsorbed on the pyrotechnic be removed prior to the preparation ofthe admixture. This may be conveniently carried out by heating thecombination of pyrotechnic and propellant (prior to pressing) attemperatures on the order of about C. for a short time, or by treatingwith a desiccant. Compression molding is then carried out, usually atabout 100 C.

The following example serves to illustrate an embodiment of theinvention. It is understood that this is given by way of exemplificationand does not in any way serve as a limitation on the invention.

Example ammonium nitrate, 62.30%; cellulose acetate, 10.40%;'

acetyl triethyl citrate, 11.85%; dinitrophenoxyethanol, 10.45%; sodiumbarbiturate, 1.00%; carbon, 3.00%; and 2,4-toluenediamine, 1.00%.

The pressed cake igniter was then subjected to burning tests todetermine its percent temperature coeflicient. This .3 coefficient iscalculated by determining the pressure generated by the igniter attemperatures of 160 F., and 65 F The difierence between the pressures at160 F. and 65 F. is then divided by the pressure at 65 F. The result isa measure of the uniformity of performance with temperature.

Seven tests were carried out on the pressed igniter and a percenttemperature coefiicient for each was calculated.

The average of the seven was 118%.

For comparison purposes, gunpowder and ammonium nitrate propellant weremixed together to form a mechanical mixture which was burned todetermine its performance. The relative proportions of each componentwere present in amounts to give approximately the same igniter pressureversus time characteristics as for the pressed igniter. Seven individualtests were carried out on the mixture. The percent temperaturecoefficient for each test was calculated and their average wasdetermined to be 152%.

The above results demonstrate the superior performance of the pressedcake igniter over an igniter which has not been compacted. The averagepercent temperature coefficient of the pressed cake igniter was 118% ascontrasted to the average of 152% for the mixture of gunpowder andpropellant which have not been consolidated into a pressed cake.

Very similar results are also obtainable from the above composition whenthe proportions of the components are within the following ranges:ammonium nitrate, 6080%; cellulose acetate, 23-12%; acetyl triethylcitrate, 1014%; dinitrophenoxyethanol, 23-12%; sodium barbiturate,0.5-5%; carbon, 0.5-5%; and 2,4-toluenediamine,

Thus having described the invention, what is claimed is:

1. As an improved igniter composition, a compacted, dense admixturecomprising a dispersion of pyrotechnic selected from the classconsisting of gunpowder, aluminum powder-alkali perchlorate, and boronpowder-potassium nitrate, in an essentially continuous phase of a solidpropellant comprising ammonium nitrate as the predominant component,between about 0.5' to about weight percent of a combustion catalyst, andabout 10 to about 40 weight percent of an oxidizable organic bindermaterial, said admixture containing about 20 to 60 weight percent ofsaid pyrotechnic and about 40 to 80 percent of said solid propellant.

2. The admixture of claim 1 wherein said pyrotechnic is gunpowder. 7

3. As an improved igniter composition, a compacted, dense admixturecomprising about 30 to weight percent of a dispersion of gunpowder inabout 50 to weight percent of an essentially continuous phase of solidammonium nitrate propellant.

4. The admixture of claim 3 wherein the propellant of said admixture hasa porosity less than about 8%.

5. The admixture of claim 3 wherein said ammonium nitrate propellantcomprises ammonium nitrate as the predominant component, between about0.5 to about 10 weight percent of a combustion catalyst, and about 10'toabout 40 weight percent of an oxidizable organic binder material.

6. The admixture of claim 5 wherein the propellant phase of saidadmixture has a porosity less than about 8%.

7. As an improved igniter composition, a compacted, dense admixturecomprising about 30 to 50 weight percent of a dispersion of gunpowder inabout 50 to 70 weight percent of an essentially continuous phase of asolid propellant consisting essentially by weight of about 60 to percentof ammonium nitrate, 8 to 12 percent of cellulose acetate, 10 to 14percent of acetyl triethyl citrate, 8 to 12 percent ofdinitrophenoxyethanol, 0.5 to 5 percent of sodium barbiturate, 0.5 to 5percent of carbon, and 0.5 to 3 percent of 2,4-toluenediamine, thepropellant of said admixture having a porosity less than about 4%.

8. Theadmixture of claim 7 wherein said gunpowder, propellant, ammoniumnitrate, cellulose acetate, acetyl triethyl citrate,dinitrophenoxyethanol, sodium barbiturate, carbon and toluenediamine arepresent in the respective weight percentages of about 45, 55, 62.3,10.4, 11.9, 10.4, 1.0, 3.0, and 1.0.

References Cited by the Examiner UNITED STATES PATENTS 2,988,876 6/1961\Valden 149--41 3,000,311- 9/1961 Stanley 149--60 X 3,017,300 1/19 62Herring 14941 3,031,347 4/1962 Philipson 149-19 X CARL D. QUARFORTH,Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,234,059 February 8, 1966 Wayne A. Proell It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 1, line 24, for "charge" read change, column 2, lines 14 and 15,for "nitrosalicylic", each occurrence, read nitrosalicyclic same column2, line 41, before "such" insert binder Signed and sealed this 3rd dayof January 1967.

ERNEST W. SWIDER EDWARD J. BRENNER Anesting Offioer Commissioner ofPatents

1. AS AN IMPROVED IGNITER COMPOSITION, A COPACTED, DENSE ADMIXTURECOMPRISING A DISPERSION OF PYROTECHNIC SELECTED FROM THE CLASSCONSISTING OF GUNPOWDER, ALUMINUM POWDER-ALKALI PERCHLORATE, AND BORONPOWDER-POTASSIUM NITRATE, IN AN ESSENTIALLY CONTINUOUS PHASE OF A SOLIDPROPELLANT COMPRISING AMMONIUM NITRATE AS THE PREDOMINANT COMPONENT,BETWEEN ABOUT 0.5 TO ABOUT 10 WEIGHT PERCENT OF A COMBUSTION CATALYST,AND ABOUT 10 TO ABOUT 40 WEIGHT PERCENT OF AN OXIDIZABLE ORGANIC BINDERMATERIAL, SAID ADMIXTURE CONTAINING ABOUT 20 TO 60 WEIGHT PERCENT OFSAID PYROTECHNIC AND ABOUT 40 TO 80 PERCENT OF SAID SOLID PROPELLANT.